That mode effectively already exists in the story mode. If you play in story mode the max corruption end doesn't happen.
Except that removes all incentive to be careful with SK use and lewd events, which -- at least in my opinion -- adds a ton to the game.
The situation I'm trying to address is where I had a moderate amount of corruption from lewd events, unexpectedly ran out of mental changes for several days (due to overlooking a prerequisite), accumulated nightly corruption over time, and ultimately capped.
If the reason for the corruption game-over is to keep people from bingeing on SK and lewd events, and the reason for the nightly corruption gain is to add challenge to a pure playthrough, then maybe a fourth suggestion would be to have the corruption gain in Aura's Mind happen only if you leave without taking an available mental change. That keep the challenge for pure players but also avoid pushing high-lewd playthroughs over the edge unintentionally.
just incentivices to do all mental changes and then use SK on everything and then ignore the corruption stat as a whole.
You're partially right. I assumed anyone wanting to play the way you described would be on Story Mode already, and so corruption game-overs existed just to make pure playthroughs challenging. So yeah, ignore my first suggestion (corruption death only if you've skipped mental changes), as this would allow someone to spam SK simply by keeping up with every mental change.
My second suggestion (Alicia can intervene when she sees her victim going over the edge) was meant to be a one-time event, sorry. I do think one bail-out wouldn't be game-breaking, and it would prevent the surprise unavoidable death like mine (i.e., a lewd playthrough with an overlooked prerequisite, leading to slow death from nightly corruption).
However, my third suggestion (maxed corruption causes stat loss, not real-life death) would cripple a character if they kept playing the way you described (i.e., spamming SK and lewd events beyond the corruption cap). So I'd still suggest that one. (Although in retrospect, there's already a mechanic kind of like this in one of the rooms. So maybe I'm 0/3.)
Anyway, it's really the nightly, unavoidable corruption gain that is the issue. Doesn't it create balancing issues for you? With constant, unavoidable corruption gain, you need to be carefully balancing the flow of blessed potions, mental change corruption dumps, etc., both to be not too fast (making the game too easy) and not too inconsistent (resulting in random deaths like mine). If you dropped the nightly corruption gain, you could keep the corruption game-over to prevent people from spamming SK and lewd events. Or maybe have nightly corruption gain happen only on nights when people skip available mental changes (which would keep pure playthroughs challenging).
Or just ignore all of this. Really, it only applies to first-time players on lewd playthroughs who didn't go Story Mode from the start, which has to be, like, six of us.